The present invention relates to an environmental control system for an aircraft.
The purpose of an environmental control system (ECS) is to supply cooled pressurized air to the cabin and the flight deck. This is typically accomplished by the use of an air cycle machine (ACM). FIG. 1 shows a schematic representation of a typical environmental control system 10 for an aircraft. Depending upon the mission point, bleed air from the engine 12 is removed from either the mid- or high-pressure stages of the high compressor 14. The bleed air is first cooled by ram air in a primary heat exchanger 16. The bleed air is then further compressed in the compressor section 18 of the air cycle machine. Additional cooling of the bleed air is performed in a secondary heat exchanger 20 using ram air as the coolant. The bleed air is then expanded to the desired pressure across the turbine section 22 of the air cycle machine. The expansion process produces the necessary work required to drive the compressor 18 and significantly drops the temperature of the bleed air. The cooled bleed air is then mixed with cabin recirculation air to maintain the temperature of the air entering the cabin at a given level.
The use of an air cycle machine for an environmental control system is a parasitic loss for the engine because it requires the extraction of engine bleed air to operate. A typical environmental control system can require as much as 5% of the core flow from the engine. Reducing the amount of engine bleed air necessary to operate an environmental control system would result in an improvement in engine specific fuel consumption.